#define _CRT_SECURE_NO_WARNINGS  1

class Solution {
public:
    string tree2str(TreeNode* root)
    {
        if (root == nullptr)
            return "";

        string str = to_string(root->val);

        if (root->left || root->right)
        {
            str += '(';
            str += tree2str(root->left);
            str += ')';
        }
        if (root->right)
        {
            str += '(';
            str += tree2str(root->right);
            str += ')';
        }

        return str;
    }
};